1. Field of the Invention
This invention relates to a component-feeding device in an electronic component-mounting apparatus of a multi-function type for mounting e.g. various kinds of supplied electronic components on a circuit board.
2. Prior Art
Conventionally, a component-feeding device of this kind is known which brings a pallet carrying thereon a single or a plurality of trays on which a lot of electronic components are juxtaposed to a pickup position of a main block of an electronic component-mounting apparatus to thereby directly feed electronic components to the main block of the apparatus. Such a component-feeding device is used for mainly feeding relatively large-sized electronic components, such as multi-lead components, and includes an elevating mechanism for lifting and lowering pallets each carrying trays thereon to selectively guide the pallets to the level of a transport passage of the main block of the apparatus, and a transport mechanism for drawing out the selected palette from the elevating mechanism to transport the same to the pickup position of the main block of the apparatus along the transport passage. Each pallet carrying the trays is set on the elevating mechanism and then lifted or lowered to the level of the transport passage to be horizontally sent to the pickup position of the main block of the apparatus by the transport mechanism. Each electronic component supplied to the pickup position is picked up and carried by a vacuum nozzle of each mounting head of the apparatus to a circuit board to be mounted thereon.
In the electronic component-mounting apparatus constructed as above, a reference level at which the mounting head carries the picked-up electronic component to the circuit board in the X-Y direction is limited by the level at which the component is supplied. More specifically, each pallet guided into the main block area of the apparatus is always set to the same level as the level of the transport passage, whereas the height of a tray(s) placed on the pallet varies with the height of electronic components juxtaposed on the tray(s). Therefore, the reference level of the mounting head is set in a manner such that the vacuum nozzle of the mounting head does not interfere with large-height trays (containing large-height electronic components).
As a result, in the conventional component-feeding device, when the tray(s) is/are guided to the pickup position by using each pallet, the difference in level between the top surface of a large-height tray and that of a small-height tray is increased with increase in the difference in height between the trays, and accordingly, except when most of the guided trays have a large height, the distance vertically traveled by the mounting head is increased resulting in an increased total tact time of mounting electronic components on each circuit board. One possible solution to this inconvenience is that the mounting head is once lifted before reaching a pallet in the pickup position only when a large-height tray is supplied i.e. carried on the pallet. This method, however, suffers from the inconvenience that the manner of control of the mounting head becomes complicated and the vacuum nozzle can be broken in case data or commands for this control are erroneously input.